Pipes traversed by pulsating flow gases



March 4, 1958 J. B ERTIN EIAL PIPES TRAVERSED BY PULSATING FLOW GASESFiled June 5, 1951 Ian/earning United States Patent PIPES TRAVERSED BYPULSATING FLOW GASES .lean' Bertin, Neuilly-sur-Seine, Paul Sarrazin,Paris, Jean 7 Le Foil, Le Pre-Saint-Gervais, and Francois G. Paris,Chaville, France, assignors to Societe Nationale dEtude et deConstruction de Moteurs dAviation, Paris, France, acompany of FranceApplication June 5, 1951, Serial No. 229,948

Claims priority, application France June 19, 1950 3 Claims. (Cl.Gil-35.6)

The exhaust pipes of explosion engines or internal combustion engines.are traversed by a pulsating flow of gas. In pulse-jet units, the sameapplies as regards :the rear tube whichforms the propulsion. jet.

The present invention relates to an improvement in such tubes traversedby a pulsating flow gas which when applied to the exhaust pipes of anordinary engine enables the filling or the scavenging inside thecylinder or cylinders of the said engine to be improved and which, whenapplied to a pulse-jet unit (which is the most important case), enablesnot only a satisfactory filling or scavenging of the combustion orexplosion chamber to be obtained, but also a marked improvement of thepropulsion output and of the thrust.

According to this invention, there is provided for the pulsating flow, aconvergent-divergent nozzle similar to a de Laval nozzle, openingdownstream into an elongated chamber of a section which is relativelylarge with respect to that of the neck of the nozzle.

This chamber may be constituted by a cylindrical or slightly conicalpipe, which may or may not be preceded by a divergent portion connectingthe surface of the nozzle to that of the pipe.

The description which follows, considered in conjunction with theaccompanying drawings, given simply by way of example, will enable themanner in which the invention is carried into effect to be readilyunderstood, the details which are apparent from the description and thedrawing obviously forming part of the said invention.

Figures 1 and 2 are diagrammatic sectional views showing two embodimentsof the invention as applied to a pulse-jet unit.

Referring to the drawing, 1 is the explosion or combustion chamber of apulse-jet unit adapted to propel a movable craft in the direction of thearrow F. Atmospheric air is admitted periodically into this chamberbetween the successive explosions or combustions by any suitable devicewhich in itself does not form the subject of the invention. Anair-admitting device has been shown diagrammatically and simply by wayof example in the drawings, which comprisesa diffuser 2 and a platecarrying valves 3 which are opened automatically between the explosionsor combustions by the pressure of the air prevailing in the diffuser 2and are closed by the pressure in the chamber 1 at the time of theexplosions or combustions.

Any other arrangement could be employed and especially a device of knowntype which does not comprise any mechanical valve but which offers aresistance to the passage of air which is smaller in the fillingdirection than in the opposite direction. The liquid fuel is admittedinto the chamber by an injector 4 and the explosion or the combustion isdetermined by a spark plug, a burner, a hot element, etc. The generatedgases are discharged from the chamber at high velocity at the rear inorder to form .the intermittent propulsion jet.

This discharge is effected, according to the invention,

through a. converging section 5 followed by a diverging section 6,thewhole constituting a nozzle similar to a de Laval nozzle. Thedivergent section 6 opens into a large-section pipe 7 which is entirelyopen at the rear at 8.

In the embodiment shown in Figure l, the pipe 7 is cylindrical, thesurface thereof forming a sudden enlargement of the section 6 of thenozzle.

The pipe 7 constitutes a sound tube which has a natural frequency ofvibration.

If this natural frequency of the pipe is tuned experimentally to thefrequency of the pulse-jet unit for a given normal rate of operation ofthe latter, for example, by suitably regulating the length l of thecylinder 7, a considerable increase in the thrust is obtained withconstant consumption of fuel, as has been proved by the tests carriedout by the applicants. This improved output results from a betterutilization of thediscontinuous kinetic energy of the hot gases escapingfrom the chamber 1. Instead ofthese gases escaping directly toatmosphere through asimple tube, as is the case with the usual devices,the arrangement described makes it possible for them to act on a supplyof fresh air which, after the previous exhaust, has entered the rearchamber 7. A major part of the kinetic energy of the hot gases istransmitted to the fresh air with an efliciency which is all the betteras the gases and the air are in stratified layers and not simplydilution and friction occur. The arrangement thus permits a transfer ofamounts of momentum between the gases and the fresh air with constantkinetic energy, this explaining the improvement of the propulsion outputwhich is observed.

Moreover, the arrangement makes it possible to extend the time ofexpulsion of the burnt gases over the most important fraction of theperiod of the pulse-jet unit and consequently to increase the thrust.

It is desirable that the section 6 of the exhaust nozzle be graduallydivergent, at least in the part near the neck.

Moreover, the following ratios have given excellent results:

The area of the cross section of the cylindrical part 7 being greaterthan three times the area of the cross section of the neck of the nozzle5, 6, the length l of the cylinder 7 is greater than a quarter of thelength L between the neck of the nozzle and the rear opening 8 of thetube 7.

The volume of the tube 7 obviously plays an important part and it is thecylinder which contains the greatest volume for a given cross-section.However, other considerations may be involved in the selection of theshape to be given to the chamber 7 and make it preferable to choose ashape different from that of a cylinder.

The applicants have obtained good results with the embodiment shown inFigure 2, in which the tube 7 comprises a first conical part 7a unitedto the outlet of the nozzle 6 and a cylindrical part 7.

Another important advantage which it is possible to obtain with theinvention is the improvement in the filling flow of a gas.

or scavenging of the explosion or combustion chamber 1 with fresh air.This result is obtained by the production, at the outlet of the nozzle6, of a divergent stream which is produced naturally in the case ofFigure 1, or caused by the shape of the wall 7a in the case of Figure 2.Upon completion of the ejection phase of the gases, this divergentstream acting on the atmosphere causes a lowering of static pressureupstream, that is to say, in the chamber 1, which facilitates thefill-ing with the fresh air entering this chamber by way of the device2, 3.

For this reason, the arrangement-described may be applied to any pipecapable o-f'serving for the pulsating As already described, it would bepossible, for example, by means of parts similar to those numbered 5, 6and 7, to adapt it to the exhaust pipe of one or more cylinders of anexplosion engine or an internal combustion engine, more especially theexhaust pipe of a two-stroke engine cylinder, whether or not the gas jetis finally used to produce a propulsive reaction.

It is obviousthat it is possibleto modify the pipes which have just beendescribed, more especially by substituting equivalent technical means,without thereby departing from the scope of the invention.

What we claim is:

1. The combination with a pulse jet engine of the type comprising aconvergent-divergent pipe designed for expanding and imparting velocityto pulses of combustion gas flowing therethrough, of an exhaust tubeextending downstream of said convergent-divergent pipe and directlyconnected thereto at one end of said tube, the other end thereof beingfreely open to the atmosphere, and facing toward the rear of the engine,said tube having a substantially uniform cross-section which issubstantially greater than the maximum cross-section of the divergentportion of said pipe.

2. The combination of claim 1 wherein the convergentdivergent pipe andthe exhaust tube have walls smoothly blending with each other.

3. The combination of claim 1 wherein the crosssection of the exhausttube is greater than three times the minimum cross-section of theconvergent-divergent pipe and the length of the exhaust tube is greaterthan one-third of the length of the divergent portion of the pipe.

References Cited in the file of this patent UNITED STATES PATENTS1,411,226 Stumpf Mar. 28, 1922 2,342,262 Franz et al Feb. 22, 19442,542,756 Draminsky Feb. 20, 1951 2,543,758 Bodine Mar. 6, 19512,573,697 Dunbar Nov. 6, 1951 2,587,100 Black Feb. 26, 1952 2.610.064Goddard Sept. 9, 1952 2,613,49 Kollsman Oct. 14, 1952 2,687,614 GoddardAug. 31, 1954 FOREIGN PATENTS 384,939 France Feb. 2], 1903 412,478France May 3, 1910 844,442 France Apr. 24, 1939 928,866 France June 16,l947

